Bitumen road paving



Patented Get. 21, 1930 'jNlTED' STATES PATIENT OFFICE- DONALD 'MoKNIGE'I'BEPBURN, or rmmnnnrnm, rnnnsrnvanm, assrenon 'ro AmEsI'rE ASPHALT- comrm'or AMERICA, or PHILADELPHIA, rnnnsrnvama,

A. CORPORATION OF NEW JERSEY a Brrumnn ROAD ravine No nmwmg.

This invention relates primarily to improvements in-that class of pavement or road surface employing a graded andbitumencoated stone aggregate free from fines and other void-filling elements and in'which the aggregate is bonded and stabilized entirely by the bitumen coating of the individual,

stones. More particularly the invention relates to improvements in the pavement forming the subject of my U. S. Patent No. 1,611,444, is

sued December 21, 1926;-and it is the principal object of the present invention to pro ,vide means whereby a't'hicker and stronger coating of bituminous substance, such as asphalt, may be made to adhere to the surfaces of the stones of the aggregate which results in a remarkable improvement in the finished stones give extremely rough surfaces. In

building roads of the above mentioned type, and where the aforesaid rough surfaces are met with, I have found it particularly desirable, if not essential, in order to properly bond the aggregate and cement the individual stones together, to provide a thicker and stronger coating of asphalt or other bitumen than would normally be required where the fracture is cleaner or than can obtained by the usual methods. This will be understood when it is stated that for a maximum cementing effect between two objects all the recesses between and in the abutting surfaces of the objects should be filled by the cementing medium.

I have discovered, in the present instance, that the bonding and cementing coating on the surfaces of the stones of the aggregate may be materially increased in thickness an improved in character by making a mortar of thebituminous cementing medium which is accomplished by adding thereto and thoroughly incorporating a predetermined quan-' tity of sand, or clean, crushed rock screenings, or the like. In-general, I prefer to use from four to eight per cent by weight of the Application filed March 81, 1927. Serial No. 180,075..

sand or rock screenings for any given amount of bitumen, although the amounts may vary beyond these limits in special cases. By this means I have found itpossible to hold from five to seven per cent, and even more, asphalt cement on the surfaces of the stone than is possible using the asphalt or other bitumen unmixed with the sand, screenings or equivalentmaterial. The bitumen mortar does not run on the stone surfaces; the aggregate does not settle in-the mixture in shipment; and the unloading and handling qualities of the paving mixture remains unaffected.

In racticing the present invention, I ma coat t e stone in accordance with the proce ure outlined in the aforesaid Patent N 0. 1,611,444, but using a larger amount of the b tumen as compared with quantity of aggregate to. be coated. Following the thorough mixing of the bitumen with the stone the sand or screenings is added and the mixing operation continued until the added material is thoroughly incorporated. The sand screenings or the like has the effect o strengtheningthe bitumen coating and permits of a greater'amount adhering to the surfaces without running. While I refer to add the sand or like material after t e stones have been thoroughly coated with the bitumen it is possible without'departure from the invention to incorporate the sand in the bitumen prior to the addition of the latter be to the aggregate Or the bitumen and sand may be simultaneously mixed with aggregate. The stone sizes of the aggregate and the method of laying the composition may also be in accordance with the procedure set forth in the atent.

, Itwi 1 be noted that I' depend entirely on an aggregateiof crushed stone with the fines under a given size removed so that my pavement is composed entirely of dust free stone.

(1. When the mixture is rolled into place and compacted, thevparticles of the aggregate or pieces of stones lie in close contact with each other, like a piece of masonry, and the VOldS between the stones are not filled with fine aggregate. The separate pieces of stone in the aggregate are pushed and wedged together, however,

in as intimate a relation as it is the voids.

possible to get them. The road'depends for cohesion and stability entirely on the bonding efl'ect of bitumen with which the stone is coated, and it is important that the cement ing medium be adequate for all the varying types of aggregate that may be used. In

order that I may properly cement, for example, two very rough surfaces together with a bitumen cement so that the surfaces are properly filled as described above, I must have a heavy coating of bitumen cement on each individual iece of stone. The heavy, stron coating of itumen provided by the presen invention meets these requirements.

but suflicient to form on each piece of aggregatea thick, stable coating of cement and sand which will not run out of the mixture when said agitation is discontinued, but will remain permanentl on and cover each of the individual pieces 0 aggregate at atmospheric temperatures and maintain said material suf ficiently loose and friable to be handled and transported until it is compacted upon the roadway.

DONALD McKNIGHT HEPBURN.

It should be further noted that my pavement is strictly a bitumen cemented road in which the designhas been carefully worked out to produce voids in the pavement in order to establish innumerable expansion joints,

and establisl a pavement that is flexible and i can move without cracking. with the expansion and contraction that takes place in the earths surface. It is therefore essential that the bitumen and sand content be kept within the amount that can be held on the stone surfaces without excess and without filling With the addition of sand or clean stone screenings preferably added to the mixture just after the asphalt has been properly distributed on the stone particles a mortar is produced increasing the thickness of the bitumen cement to such an extent that I can hold from five per cent (5%) t0 ten er cent (10%) more asphalt on the stone sur aces and produce a tighter bond and an improved material in seahn qualities without appreciably reducing to voids in my pavement'or. reducing the non-skid qualities of my pavement.

In practice, I have noteda marked im provement in roads made with stone aggregate coated in accordance with my invention;

and this improvement is noted not only in the ment in a fluent,mobile condition by thor- .oughly agitating said aggregate in the presence of said fluid cement, the quantity of cement so admixed with the aggregate being substantially greater than what would remain on the aggregate were said agitation to cease,

and then add ng to said mobile cement on said aggregate still under a itation a quantity of clean, sandy fines insu cient to appreciably reduce the voids in the finished pavement, 

